The present invention generally relates to power sources, and more particularly is concerned with power sources for use in pulsed operations at microwave frequencies, which are made by connecting IMPATT diodes electrically and thermally in series.
Impact ionization avalanche transit time (IMPATT) diodes have many uses, but they are best known for their abilities to produce negative resistances and act as reliable solid-state sources of power at microwave frequencies. A similarity in all IMPATT diodes is the fact that they contain at least a single junction between a P-type semiconductor and an N-type semiconductor. Also, when these diodes operate, it becomes necessary to provide a good heat sink nearby to prevent burn-out of the P-N junction. A brief description of the operation, construction and function of IMPATT diodes is given in Sze, Semiconductor Devices, Physics and Technology, published in 1985 by John Wiley .differential. Sons, New York, N.Y., in chapter 6.2 at pages 229-234 (inclusive) which is hereby incorporated herein by this reference.
Temperature often affects performance of IMPATT diodes. The temperature characteristics of IMPATT diodes have been the subject of much research, and have been discussed in the following articles which are incorporated herein by this reference: Olson, Temperature Transients in IMPATT Diodes, IEEE Electron Devices, Vol. ED-23, No. 5, May, 1976; Olson, A Mechanism for Catastrophic Failure of Avalanche Diodes, IEEE Electron Devices, Vol. ED-22, No. 10, Oct. 1975; and Diebold, Temperature Rise of Solid Junctions under Pulse Load, AIEE, Vol. 76, Part 1, Communications and Electronics, Nov. 1957.
In some applications, it is desirable to electrically connect several IMPATT diodes in series in order to achieve a certain predetermined power characteristic. Also, in certain applications, the diodes are often not operated in a continuous wave signal mode, but they are subjected to an incident pulsed signal. When considering that diodes, which are connected electrically in series and subjected to a pulsed signal, have junction temperatures constantly varying in time, and further considering the variable performance of IMPATT diodes as a function of temperature, it is frequently desirable to have the temperature of the individual diodes track together in time.
In one arrangement used in the past, several IMPATT diodes were electrically connected in series, and were typically placed thermally in parallel, for example, side by side on a single heat sink. In such configurations, the single heat sink serves each diode equally. The lateral separation between the diodes and the overall size and surface area of the heat sink necessary for proper operation depend upon many factors including the heat generated by the diodes, the heat sink composition, the diode diameter, and the overall environment.
While this method of power generation at microwave frequencies, or variations of it, have enjoyed extensive use in the past, they have several major drawbacks. One problem with arranging the several IMPATT diodes in a parallel thermal configuration is that the then-requisite electrical connections needed to serially connect the separated diodes creates a parasitic resonance in the structure. Furthermore, with the current trend toward miniaturization of electronics equipment, the conventional power source with a single planar heat sink is increasingly less attractive, because such a configuration is often too large and cumbersome.
Consequently, a need exists for improvement in power sources for use at microwave frequencies in pulsed operations, which result in the reduction of parasitic resonance in the structure while concurrently reducing the planar surface area, the overall size and weight of the power source, and concomitantly providing for improved performance by a relative tracking together in time of the temperature of the individual diodes during pulsed operations.